1. Field of the Invention
This invention relates to methods and apparatus for the remediation of particulate matter and toxic flue gas pollutants in transit in a flue gas stream, and in particular to methods and apparatus for removal of materials and pollutants, such as sulfur dioxide, from flue gases produced in coal fired power plants, and the like, by forcing and promoting a reaction between the pollutants and selected sorbent materials.
2. Prior Art
In the combustion of fossil fuels, as for power generation, a variety of particulate matter and gaseous pollutants, some of which are toxic, are produced and discharged as flue gas. Among which are oxides of sulphur, including sulphur dioxide, SO2 oxides of nitrogen and volatile organic compounds. The oxides of sulphur, particularly sulphur dioxide SO2 are generally considered as the most serious and are toxic pollutants. To remove flue gas pollutants, a number of pollution control systems have been developed that remove fine particulate matter and submicron size particles. Some such systems rely on electrostatically charged sorbent particles to attract and agglomerize with unlike charged particles in the flue gas stream, providing particles of a sufficient size to be removed in a moving fluidized bed, by passage through a bag house, in a centrifuge system, or the like. Examples of several such systems that one of the present inventions is a co-inventor of are found in U.S. Pat. No. 5,308,590; 5,312,598; and 5,332,562.
Functionally and structurally distinct from such electrostatic charging system, a system for promoting a reaction between pollutants and sorbent material by providing compaction and mixing of the agglomerized particles of pollutant and sorbent materials for separation in a conventional bag house, centrifuge, or the like, is set out in U.S. patents to one of the present inventors, U.S. Pat. Nos. 5,723,099 and 5,795,549. The above '099 and '549 patents teach a mechanical mixing of sorbent materials into a flue gas stream utilizing a fan or impeller, and a passing of the mixed flow through a venturi. The present invention improves upon these patents by providing a unique injection system for passing a counter-current flow of sorbent materials, under pressure, into the flue gas stream that results in a greatly improved mixing efficiency, and which mixing continues over a long residency period for thorough mixing and agglomerizing together of the sorbent and pollutant particles. Further, the invention measures and controls mix moisture content after flue gas and sorbent mixing to, as needed, add moisture, as a fine pressurized water spray into the flow, so as to obtain an ideal moisture content of the agglomerized particles that makes possible the removal of essential all the pollutant particles from the gas stream as in a bag house, or particulate removal system.
In addition to the above cited U.S. patents to one of the present inventors, a number of systems have been developed and employed that provide for a remediation of toxic flue gases utilizing sorbent material compaction, none of which, however, anticipate the invention. For example, a U.S. Pat. No. 4,061,476 to Holter, et al, provides for delivery of a sorbent material into a gas stream and employs a venture that reduces the passage cross section to stimulate mixing of a sorbent that is then reacted with pollutants in a gas stream. The invention is, of course, distinct from the mixing system of the '476 patent as it relies upon a pressurized flow of sorbent materials injected into a flue gas stream counter-current to the direction of the flue gas flow to provide turbulence and mixing. Like the '099 and '549 patents of one of the present inventors, the Holter, et al '476 patent, and U.S. Patents to Bortz, et al., U.S. Pat. No. 5,165,902; to Teller, U.S. Pat. No. 4,271,134 and to Kimura, U.S. Pat. No. 4,645,653, that is shown also in a European Patent Application, No. 0,226,863, all involve moisturizing of the sorbent materials prior to passage into the flue gas stream. None, however, provide for measuring the moisture content of the mix of sorbent materials and flue gas constituents, like the invention. Nor do they provide for adding water thereto, as needed, to obtain an optimum moisture content of the mix prior to separation of the agglomerized sorbent and pollutant particles as in a bag house, or like particulate removal system.